1. Field of the Invention
The present invention relates to diode switched circuits for providing an adjustable phase shift network, of the type constructed by miniaturized circuits utilizing microstrip delay line structures and with phase increment adjustments performed by the switching of diode "chips" mounted to the delay line structure in a manner of high density packaging. More particularly, the invention relates to an improved electrical design of such a network.
2. Description of the Prior Art
In diode switched phase shifters, of the type referred to, changes in phase shift are accomplished by altering the D.C. current distribution to the diodes in the network. These diodes present either short circuits or open circuits to the R.F. energy, depending upon whether they are conducting or non-conducting. In the prior art, the diodes are from a D.C. standpoint, individual diodes and controlled by individual driver circuits which provide their forward bias. Another known practice, where the functions of several diodes are identical, is for such several diodes to be biased from the same driver source, with the diodes connected in parallel relative to this source. A typical configuration of the driver has the D.C. forward bias voltage applied across the diode or diodes through a collector-emitter path of a transistor switch. An individual network of voltage source and transistor switch is applied to each diode or each of several diodes having the same function.
In applications where source power is at a premium such as in satellites, or where power dissipation can cause severe thermal problems such as in compact airborne radars, these prior art approaches dissipate relatively high amounts of power. This is because a minimum of 5 volts for the diode forward bias source is desirable for reasons of regulation and power supply efficiency. The required diode current is a function of the diodes, and the total average power required in a network will be: EQU P = N .multidot. I .multidot. V
where:
I = required diode current; PA1 N = average number of diodes conducting; and PA1 V = source voltage.
In a typical case the diode current would be 100 ma. For a 10 diode circuit the power source requirement would be 5 watts. Accordingly, there has been a continuing effort to obtain reductions in the power consumption required for operation of a diode switched phase shifter networks.
In addition to the above discussed needs for achieving lower power dissipation in such phase shifter networks, there is a continuing need for providing such networks which have wider bandpass characteristics, and lower R.F. insertion losses.